1. Field of the Invention
The present invention relates to an improved electronic system for use with low-level analog sensors. More specifically, the present invention relates to a system for transmitting electrical signals bi-directionally between a remote sensor unit and a control terminal unit along a single pair of unshielded transmission lines.
2. Description of Prior Art
Heretofore, low-level analog sensors such as hydrophones, geophones, and microphones, disposed at remote locations with respect to a central terminal unit have experienced various problems in the transmission of signals between the sensors and the terminal units, and the implementation of control functions at the sensor units under direction of the central terminal unit. For example, the long transmission lines which couple the remote sensor units and the central terminal units are subject to electromagnetic interference (EMI) which degrades the quality of the signals. In addition, transients such as lightning, may frequently damage the sensor units. It is also a problem to provide power to the remote sensor units to drive all of the associated electronics. For example, the low level analog output of the sensors requires amplification by electronic amplifiers before transmission to the central terminal unit. Power for these amplifiers has traditionally been supplied by batteries at the sensors or by multi-conductor cables running from the central terminal unit.
It is also necessary to be able to adjust and calibrate the sensor units and associated electronics preferably from the central terminal units. However, when control functions are initiated at the central terminal unit, it has heretofore been necessary to provide additional control lines running from the central terminal unit, adding to the system complexity and increasing the probability of system noise.
Prior art systems have also traditionally required transmission lines with suitable shielding or other circuit components and techniques to reduce electromagnetic interference (EMI).